Last March, my wife and I were on Mardi Gras without Cheers. On sea days, we averaged 6 drinks each. On port days, we averaged 3-4 drinks. Drinks were almost all cocktails. After adding up all the drinks, we saved a total of $150 vs Cheers. However, we purchased 1 or 2 bottles of wine during the week and had 2-12 packs of bottled water delivered to our stateroom, which I didn't take into account. We also didn't order any specialty coffees or soda.
We have purchased Cheers (1st time) for our next sailing. We will buy wine by the glass this trip. I feel it will be worth it for us, but we shall see.